Pulse motor control system

ABSTRACT

A control means is provided for controlling a hydraulic cylinder to effect translatory movement of a supported load. The control includes a null seeking valve arranged to receive input signals from valve motive means and feedback signals from a load following non-rotating probe. The valve includes a first element which is fixed to provide a reference base and a second element which is operably connected to the non-rotating probe and which moves away from the null position by moving relatively to the non-rotating probe in response to input signals and back to the null position by moving with the probe in response to loadfollowing movement of the probe.

United States Patent [191 Ponter [451 Apr. 2, 1974 [73] Assignee: Ritter Engineering Company,

Pittsburgh, Pa.

[22] Filed: May 1, 1972 21 App]. No.: 249,400

Primary Examiner-Paul E. Maslousky Attorney, Agent, or Firm-McNenny, Farrington, Pearne & Gordon [57] ABSTRACT A control means is provided for controlling a hydraulic cylinder to effect translatory movement of a supported load. The control includes a null seeking valve arranged to receive input signals from valve motive means and feedback signals from a load following non-rotating probe. The valve includes a first element which is fixed to provide a reference base and a second element which is operably connected to the nonrotating probe and which moves away from the null position by moving relatively to the non-rotating probe in response to input signals and back to the null position by moving with the probe in response to loadfollowing movement of the probe.

3 Claims, 2 Drawing Figures '1 PULSE MOTOR CONTROL SYSTEM The' present invention relates to control means for a hydraulic actuator for providing translatory movement of a load from a reference position to a preselected, displaced position and, more particularly, to a closed-loop control means comprising a null seeking control valve operably connected to a load-following, non-rotating screw probe.

The prior art discloses various control means for achieving closed-loop control of load bearing hydraulic cylinders. US. Pat. No. 2,910,967 to Rosebrook discloses a rotating signal shaft operably connected to a spool valve arranged to port a hydraulic cylinder to thereby control the relative positions of the work tables of a milling machine. The spool of the valve is threadedly engaged with a signal shaft which is rotated to provide axial displacement of the spool to cylinder porting positions within the fixed valve body. The signal shaft is journaled to the work table being moved and is carried thereby as a follower, to provide the spool with a feedback signal corresponding to the movement of the work table. The input signal and the feedback signal are both transmitted via the signal shaft, the former by rotation thereof, and the latter by following translation thereof.

The present invention provides a closed-loop control which transmits the input signal independently of the follower member, which therefore may'simply be a non-rotating threaded rod depending or projecting from the load in a direction generally parallel to the direction of actuation of the controlled cylinder. The remainder of the control may be a self-contained unit which simply receives the non-rotating threaded rod. This self-contained unit may be directly and compactly packaged with or mounted to the hydraulic cylinder being controlled. In the illustrated embodiment, the control comprises a spool valve having its housing fixed to provide a reference base and its spool valvably movable from a null position to port associated ends of a hydraulic cylinder in response to input and feedback signals. The spool valve is arranged so that the input and feedback signals cause concurrent movement of the spool in opposite axial directions. Accordingly, the movement of the spool is the algebraic result of the countervailing input and feedback signal movements.

The spool is threadedly engaged with the nonrotating threaded rod or screw probe and arranged for two types of movements resulting from the input and feedback signals. In response to an input signal from setting means such as a stepping motor, the spool rotatably advances a preselected distance along the nonrotating'screw probe in a first direction, from the null position, to appropriately port the cylinder and thereby cause displacement of the load. Upon movement of the load, the spool is bodily carried by the screw probe in the opposite direction, towards the null position, in response to the following movement of the screw probe. Such movement constitutes the feedback signal.

The spool will be returned to the null position only when the screw probe has carried the spool a distance equal to the distance of the preselected rotational advance thereof and the load has been displaced a corresponding distance. When the spool is in the null position, the system will be in equilibrium and the load static. lf the load starts to drift, the following movement of the screw probe will carry the spool from the null position so as to correctively port the cylinder until the load is returned to the preselected position and the spool is returned to the null position.

A number of hydraulic cylinders may be provided with control means according to the present invention in a plural system in order to uniformly move one or more loads in response to a common input signal. In such a plural system, the control means assure load movements at uniform rates and maintenance of the preselected displacements by virtue of the individual cylinder feedback signals. Setting means for the several controls, such as stepping motors,may be controlled by simple open-loop electrical circuitry.

The control means of the present invention achieves closed-loop control and accuracy without the use of expensive, electrical closed-loop circuitry. Further, the control means is structurally efficient in comparison with the teachings of the prior art, and its simplicity of installation permits it to be usedin many existing hydraulic actuators.

FIG. 1 is an elevational view of a load being supported by a hydraulic cylinder provided with control means in accordance with the present invention; and

FIG. 2 is an elevational view, on an enlarged scale and partially in section, showing the details of the control means. 1

Referring to FIGS. 1 and 2, there is shown a load 10 supported in a fixed position by a hydraulic cylinder 12 having a cylinder rod 13. The hydraulic cylinder is provided with a closed-loop control means comprising a control valve 14, a pulse or stepping motor 16, and a non-rotating following screw 18. The following screw is secured to the load by means of a mounting flange 20, and fixed against rotation by means of a set screw 21.

The control valve 14 comprises a valve body or housing 14a and a valve spool 14b which is threadedly engaged with the following screw. The valve body is fixed to the hydraulic cylinder 12 and has a mounting bracket 17 attached to it for supporting the motor. The valve body provides a reference base for the translatory movement of the load 10 as will become more apparent hereinafter. It should be appreciated that the control valve may be supported by any convenient means and that it is only necessary for such support means to maintain the valve body in a stationary position in order to provide a reference base. Alternatively, the valve spool may be retained in a stationary position in order to provide a reference base instead of the valve body,

The spool 14b is coaxially disposed within the valve body and mounted therein to permit axial movement in either direction relative to the valve body. To that end, the spool is mounted within the valve body by means of oppositely. disposed compression springs 22 and 24 and associated mounting collars 26 and 28 which limit the axial movement of the spool relative to the valve body. The compression springs and collars are mounted externally of the valve body and facilitate assembly of the valve.

The valve spool is journaled within the valve body by means of ball bearings 30 and 32 to pennit relative rotation which results in the axial displacement of the spool in a screw-type movement. Accordingly, the spool may be rotated from a reference or datum angular position corresponding to the reference base provided by the valve housing to a preselected angular or axial displaced position.

The valve spool 14b is effectively a three land spool having a central land 34 defined by spool groves 34a and 34b, and end lands 36 and 38. The valve body 14a is provided with a pressure groove 40 which is connected to a hydraulic pressure source (not shown) by means of an inlet port 40a. A hydraulic operating pressure is maintained in the pressure groove at all times during the control operation.

Axially disposed above the pressure groove as shown in FIG. 2, there is a cylinder supply groove 42 having a port 42a which is connected to the bottom of the hydraulic cylinder 12 by means of a hydraulic line 44 (FIG. 1). A cylinder exhaust groove 46 is located adjacent to the supply groove 42 for purposes of relieving the hydraulic pressure at the bottom of the cylinder 12 when it is desired to retract the cylinder rod 13. Ac-

cordingly, the groove 46 is provided with a port 46a which is connected to the reservoir of the pressure supply means (not shown).

Axially spaced below the pressure groove 40 as shown in FIG. 2, there is a cylinder supply groove 48 having an associated port 48a connected to a hydraulic line 50 (FIG. 1) for pressurizing the top of the hydraulic cylinder. An exhaust groove 52 having a port 52a is similarly provided for relieving the hydraulic pressure in the top of the cylinder when it is desired to extend the cylinder rod and raise the load.

As shown in FIG. 2, the control valve is in the null position and all of the valve ports are closed. Accordingly, the system is in equilibrium and the load is at rest when the control valve is in the null position.

As previously indicated, the valve spool 14b is rotatably advanced along the following screw out of the null position in response to an input signal. To that end, the output shaft 54 of the stepping motor 16 is provided with a drive gear 56. The drive gear 56 is arranged to engage a driven gear 58 which is keyed to the valve spool 14b. It should be noted that the maximum translatory movement of the valve spool during the control operation is not sufficient to cause disengagement of the gears 56 and 58.

Assuming the system to be at rest and that it is desired to raise the load, the operation of the control means is initiated by a command input pulse to the stepping motor. In response to the input pulse, the stepping motor will cause the drive gear 56 to rotate in a clockwise direction as viewed from the gear end of the output shaft. The driven gear 58 will rotate in a counter-clockwise direction and the valve spool 14b will be displaced downwardly from the null position as shown in FIG. 2.

Upon the initiation of displacement of the valve spool, the pressure groove 40 will be placed in communication with the cylinder supply groove 42 by means of the spool groove 34a and the bottom of the hydraulic cylinder 12 will be pressurized. Simultaneously, the cylinder supply groove 48 will be placed in communication with the cylinder exhaust groove 52 by means of spool groove 34b. Accordingly, the bottom of the hydraulic cylinder 12 will be pressurized, the top exhausted, and the cylinder rod 13 extended to raise the load 10.

As the load is raised, the following screw 18 is moved a corresponding distance and bodily carries the valve spool 14b along with it and back towards the null position. Consequently, the cylinder will continue to raise the load until the load is displaced a distance equal to the total downward displacement of the valve spool resulting from the input pulse, that is, until the displacement of the load catches up" to the displacement of the valve spool. When this occurs, the valve spool is again in the null position and all of the valve ports are closed.

If any change in the position of the load occurs after equilibrium is reached, the control means immediately self-corrects and returns the load to the preselected position. For example, if the load drifts downward due to load variation or internal leakage, the following screw correspondingly drifts and displaces the valve spool from the null position. In the same manner as indicated above, the hydraulic cylinder is again ported so as to cause the cylinder rod to extend until the downward drift is corrected and the valve spool is returned to the null position.

To lower the load, the direction of the stepping motor is of course reversed so as to advance the valve spool in an opposite direction along the following screw and port the hydraulic cylinder in a manner opposite to that described above.

What is claimed is:

1. Hydraulic actuator control means for controlling translatory movement of a load from a datum translatory position to any selected one of a number of measures of translatory displacement from said datum position, comprising a control valve housing, a valve spool sealingly received within the housing for nonvalving rotating motion and for valving translatory motion relative to the housing, a non-rotating feedback screw coaxially threadedly received within the valve spool, means mounted with the housing for rotating the valve spool from a datum angular position, corresponding to said datum translatory position of the load, to any selected one of a number of measures of angular displacement corresponding in one to one relationship with said measures of translatory displacement of the load in a direction to tend to establish actuation of a hydraulic cylinder controlled by the control valve, said feedback screw being supportable by the load in an orientation to be translated by said translatory displacement of the load so as to in turn translate the valve spool in a direction to tend to clo se off actuation of a hydraulic cylinder controlled by the control valve.

2. Hydraulic actuator control means as set forth in claim 1 wherein said valve spool is resiliently mounted within said valve housing by a pair of oppositely disposed compression springs.

3. Hydraulic actuator control means as set forth in claim 2 wherein said means for rotating the valve spool comprises a stepping motor having a drive gear engaged with a driven gear keyed to said valve spool. 

1. Hydraulic actuator control means for controlling translatory movement of a load from a datum translatory position to any selected one of a number of measures of translatory displacement from said datum position, comprising a control valve housing, a valve spool sealingly received within the housing for non-valving rotating motion and for valving translatory motion relative to the housing, a non-rotating feedback screw coaxially threadedly received within the valve spool, means mounted with the housing for rotating the valve spool from a datum angular position, corresponding to said datum translatory position of the load, to any selected one of a number of measures of angular displacement corresponding in one to one relationship with said measures of translatory displacement of the load in a direction to tend to establish actuation of a hydraulic cylinder controlled by the control valve, said feedback screw being supportable by the load in an orientation to be translated by said translatory displacement of the load so as to in turn translate the valve spool in a direction to tend to close off actuation of a hydraulic cylinder controlled by the control valve.
 2. Hydraulic actuator control means as set forth in claim 1 wherein said valve spool is resiliently mounted within said valve housing by a pair of oppositely disposed compression springs.
 3. Hydraulic actuator control means as set forth in claim 2 wherein said means for rotating the valve spool comprises a stepping motor having a drive gear engaged with a driven gear keyed to said valve spool. 